[bazel] Improve runfiles handling (#10098)

we can't use runfiles directory on Windows due to path lengths, so swap
to manifest strategy. Parsing the manifest is a bit complex and the
format is changing in Bazel upstream, so pull in the official Rust
library (via a small hack to make it importable...) and cleanup all the
associated logic to work cleanly in both bazel and cargo without extra
confusion

codex-rs/exec/tests/suite/resume.rs

@@ -113,7 +113,7 @@ fn exec_fixture() -> anyhow::Result<std::path::PathBuf> {
 }
 
 fn exec_repo_root() -> anyhow::Result<std::path::PathBuf> {
-    Ok(find_resource!(".")?)
+    Ok(codex_utils_cargo_bin::repo_root()?)
 }
 
 #[test]